In many synchronous generators it is highly desirable to eliminate brushes since they frequently require maintenance and/or replacement, and are perhaps the single weakest point in the system in terms of breakdowns. Moreover, by its very nature, the electrical path between a brush and a commutator is subject to arcing which may introduce transients into the electrical energy being produced, which in turn, may interfere with proper operation of some types of electrical loads on the generator.
A typical brushless generator has three distinct generating systems including a main generator, an exciter, and a permanent magnet generator. The permanent magnet generator includes permanent magnets for establishing a magnetic field which is employed to induce current in a set of windings, which in turn is employed after rectification to generate a magnetic field in the exciter. The magnetic field in the exciter is in turn employed to induce an even higher level of current, typically three-phase alternating current, which is then rectified and employed to generate the magnetic field for the main generator by flowing the DC current through the main field winding of the generator system.
In order to avoid the use of brushes, it is necessary that the magnetic field in the main generator be in the rotor so that the output of the system can be taken from the stator of the main generator. In order to generate a suitable magnetic field in the rotor, it is necessary to utilize direct current, as opposed to alternating current, for the same. Since the output of the exciter is an alternating current, this current must be rectified by a rectifier assembly to direct current. And, again, in order to avoid resort to brushes, it is accordingly necessary that the rectifier assembly interconnecting the exciter and the main generator field winding be carried by the rotor of the generator. Such a rectifier assembly should also be capable of withstanding high centrifugal loading.
In certain configurations, the exciter armature is delta connected or WYE connected with a floating neutral, and the rectifier assembly is a full-wave diode bridge. One such full-wave rectifier assembly is disclosed in commonly owned U.S. Pat. No. 4,628,219, issued Dec. 9, 1986 to Troscinski, the details of which are herein incorporated by reference.
However, in certain other configurations, the rectifier assembly comprises a half-wave rectifier, and the exciter armature is WYE connected to positive and negative input terminals of the main generator field through the use of this rectifier assembly. Specifically, the exciter armature has three power leads and one neutral lead. The rectifier assembly has three diodes enclosed in a housing and coupled as a half-wave bridge. The diodes are individually coupled to their respective exciter armature power output leads and mutually coupled to the generator field positive input terminal, and the exciter armature neutral lead must be coupled to the generator field negative input terminal. In these configurations, means must be provided for electrically coupling the exciter armature neutral lead to the generator field negative input terminal.
Coolant oil is typically provided to the rectifier assembly housing to remove heat from the diodes. Accordingly, the rectifier assembly must remain sealed to prevent any leakage of the oil at unwanted locations.
The present invention is directed to overcoming one or more of the above problems.